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Sediments from the paleoequatorial Pacific record the paleomagnetic field with high-fidelity and contain cyclic variations in chemical and physical properties that can be astronomically tuned, as has been shown from past Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) cruises, e.g., Legs 85, 138, 198, and 199. In an effort to fill gaps from past coring and to construct complete stratigraphic sections spanning the Cenozoic, Integrated Ocean Drilling Program (IODP) Expeditions 320 and 321 cored sediments along a Pacific Equatorial Age Transect (PEAT) earlier this year. A total of 23 holes at 8 Sites (Sites U1331 through U1338) were cored, recovering 6,141 m of sediment (Preliminary Reports are available at http://iodp.tamu.edu/publications/PR.html). Initial paleomagnetic results from Expedition 320 include measurements at 56,222 intervals along ~2000 split-core sections, as well as detailed progressive alternating field (AF) and thermal demagnetization of over 400 discrete samples (7 cm3 cubes). The cleaned paleomagnetic data were characterized by shallow inclinations, consistent with the sites being near the paleoequator, and by 180° alternations in declination downhole, reflecting magnetic polarity zones. The resulting magnetostratigraphies, which are used to develop initial age models for the drill sites, yield 803 dates ranging from 51.743 Ma (the base of Chron 23n.2n at Site 1331) to the present (Chron C1n; 0 to 0.783 Ma at Site U1335). In addition, 83 short polarity intervals were observed that might correspond to cryptochrons or geomagnetic excursions. We will discuss initial efforts to further resolve the PEAT magnetostratigraphies and to integrate them with bio-, chemo-, and cyclo- stratigraphies from the equatorial Pacific and elsewhere in order to improve and extend astronomical calibration of the geologic timescale.

2. Adler, Ruth E.

et al.

Polyak, Leonid

Ortiz, Joseph D.

Kaufman, Darrell S.

Channell, James E. T.

Xuan, Chuang

Grottoli, Andrea G.

Sellen, Emma

Stockholm University, Faculty of Science, Department of Geology and Geochemistry.

Sediment core HLY0503-8JPC raised by the HOTRAX'05 expedition from the Mendeleev Ridge was analyzed for multiple lithological, paleontological. and stable-isotopic proxies to reconstruct paleoceanographic conditions in the western Arctic Ocean during the Late Quaternary. The core, extensively sampled in the upper 5 m, reveals pronounced changes in sedimentary environments during the ca. 250 kyr interval encompassing Marine Isotopic Stages (MIS) 1 to 7. An estimated average resolution of 500 yr/sample, at least for the last glacial cycle including the last interglacial, provides more detail than seen in other sedimentary records from the western Arctic Ocean. The age control is provided by C-14 and amino acid racemization measurements on planktonic foraminifers and correlations with the stratigraphy developed for the central Lomonosov Ridge and with glacial events at the Eurasian Arctic margin. Cyclic variations in lithology combined with foraminiferal abundance and stable-isotopic composition indicate profound changes in hydrographic and depositional environments between interglacial-type and glacial-type periods apparently reflecting a combination of 100-kyr and precessional time scales. This periodicity is complicated by abrupt iceberg- and/or meltwater-discharge events with variable (Laurentide vs. Eurasian) provenance. The proxy record from the interval identified as the last interglacial (MIS 5e), which may aid in understanding the future state of the Arctic Ocean, indicates low ice conditions and possibly enhanced stratification of the water column.

Quaternary sediments from Middle Valley and the eastern flank of the Juan de Fuca Ridge recovered during the Ocean Drilling Program Legs 139 and 168 have been analyzed for total hydrolyzable amino acid concentrations, individual amino acid abundances and stereochemistry in order to evaluate the effects of hydrothermal stress on the decomposition of sedimentary amino acids. In near surface sediments, amino acids account for up to 3.3% of the total organic carbon content and up to 12% of the total nitrogen content. The non-protein amino acid b-alanine and g-aminobutyric acid become increasingly abundant with depth in low temperature holes (Leg 168) as a result of enzymatic decarboxylation of aspartic acid and glutamic acid, respectively. The decomposition of amino acid in high temperature holes (Leg 139) is enhanced with depth and the amino acid patterns indicates that most amino acids are incorporated into geopolymers and that condensation results in increased stability of some amino acids.

The effects of low temperature hydrothermal activity on microbially mediated organic matter diagenesis were studied by comparing depth concentration profiles of interstitial sulfate and methane of Holes 1023A, 1024B, 1025B and 1028A, ODP Leg 168. Diffusional exchange between sulfate-rich basement fluids and pore-waters increases the interstitial sulfate concentrations with depth below local sulfate minima caused by bacterial sulfate reduction. The effects of diffusional processes on pore-water chemistry in the sediment column is reflected by the inhibition of methane production and is largely dependent on sediment thickness.

The decomposition of alanine, leucine, aspartic acid and serine in aqueous solutions was studied at 200oC and 50 bar with the purpose of evaluating the effect dissolved oxygen on decomposition rates. The redox buffering mineral assemblage pyrite-pyrrhotite-magnetite was used to constrain the oxygen fugacity to geologically realistic values. Comparisons between results obtained from buffered and nonbuffered runs show that the decomposition is faster for most amino acids but serine in nonbuffered experiments.

12.

Andersson, Eva

et al.

Stockholm University, Faculty of Science, Department of Geology and Geochemistry.

Holm, Nils

Stockholm University, Faculty of Science, Department of Geology and Geochemistry.

One sediment core from the Jarnavik bay in Blekinge archipelago has been investigated for its content of pollen and diatoms and its chemical properties. Two levels were also dated by radiocarbon. Based on the results the sediment sequence analysed has been divided into three environmental units largely corresponding to the lithology of the sequence. A lowermost unit consisting of weakly varved and homogeneous clay was deposited during the end of the brackish phase of the Yoldia Sea at a moderate water depth. On top of this unit a gyttja-clay unit was deposited. The onset of the deposition of this unit has been dated to c. 11 100 cal. yrs. BP. An increasing organic production and increased terrestrial influence is recorded in the chemical data and a very shallow water depth is indicated in the pollen and diatom flora. These results point to conditions in a bay probably isolated from the Yoldia Sea. A local tentative shore displacement curve have been constructed and it is proposed that this unit represents the low stand at c. -18 m during the Yoldia Sea stage in this part of the Baltic Sea basin. The uppermost unit consists of homogeneous clay with a low content of organic carbon. An increasing water depth is indicated by the composition of both pollen and diatoms. The diatom flora also displays an increase in freshwater species. This environmental change was probably the result of a transgression in the beginning of the Ancylus Lake stage.

The Earth’s oceans are important regions of research exploration because they play key roles in driving the Earth’s climate, are very geologically active and preserve sedimentary and rock records that provide a detailed climate and tectonic history of the Earth over the last 200 million years. The Integrated Ocean Drilling Program (IODP) is the only international research program that provides scientists from all over the world with long, continuous sediment and rock records to study the Earth’s history in these very important regions. The European Consortium for Ocean Research Drilling (ECORD) is the European branch of IODP, which also includes scientists from the USA, Japan, the People’s Republic of China and South Korea.

The goal of the ECORD workshop is to provide teachers with information and material that can be used to enhance science classes for school students and to illustrate the excitement found in ocean research drilling.

Scientific talks designed specifically for school teachers by leading IODP scientists will highlight selected ocean drilling research topics important for humanity such as natural resources (gas hydrates), natural hazards (earthquakes, volcanic activity, undersea landslides and tsunamis) and natural climate variation (growth and decline of ice sheets and sea level change).

The ECORD teacher’s workshop will also provide teachers with background speeches that introduce the highly specialized IODP research ships that drill sediment and rock cores for scientific studies, as well as an introduction to the international IODP websites where teachers and students can obtain scientific results, real-time information about current research cruises, and learning materials for use in their classrooms.

18.

Backman, Jan

et al.

Stockholm University, Faculty of Science, Department of Geology and Geochemistry.

The Arctic Coring Expedition (ACEX) proved to be one of the most transformational missions in almost 40 year of scientific ocean drilling. ACEX recovered the first Cenozoic sedimentary sequence from the Arctic Ocean and extended earlier piston core records from ≈1.5 Ma back to ≈56 Ma. The results have had a major impact in paleoceanography even though the recovered sediments represents only 29% of Cenozoic time. The missing time intervals were primarily the result of two unexpected hiatuses. This important Cenozoic paleoceanographic record was reconstructed from a total of 339 m sediments. The wide range of analyses conducted on the recovered material, along with studies that integrated regional tectonics and geophysical data, produced surprising results including high Arctic Ocean surface water temperatures and a hydrologically active climate during the Paleocene Eocene Thermal Maximum (PETM), the occurrence of a fresher water Arctic in the Eocene, ice-rafted debris as old as middle Eocene, a middle Eocene environment rife with organic carbon, and ventilation of the Arctic Ocean to the North Atlantic through the Fram Strait near the early-middle Miocene boundary. Taken together, these results have transformed our view of the Cenozoic Arctic Ocean and its role in the Earth climate system.

The common assumption that chloride (Cl-) is conservative in soils and can be used as a groundwater tracer is currently being questioned, and an increasing number of studies indicate that Cl- can be retained in soils. We performed lysimeter experiments with soil from a coniferous forest in southeast Sweden to determine whether pore water residence time and nitrogen and Cl- loads affected Cl- retention. Over the first 42 days there was a net retention of Cl- with retention rates averaging 3.1 mg Cl- m(-2) d(-1) (68% of the added Cl- retained over 42 days). Thereafter, a net release of Cl- at similar rates was observed for the remaining experimental period (85 d). Longer soil water residence time and higher Cl- load gave higher initial retention and subsequent release rates than shorter residence time and lower Cl- load did. Nitrogen load did not affect Cl transformation rates. This study indicates that simultaneous retention and release of Cl- can occur in soils, and that rates may be considerable relative to the load. The retention of Cl- observed was probably due to chlorination of soil organic matter or ion exchange. The cause of the shift between net retention and net release is unclear, but we hypothesize that the presence of O-2 or the presence of microbially available organic matter regulates Cl- retention and release rates.

31.

Bastviken, David

Stockholm University, Faculty of Science, Department of Geology and Geochemistry.

Methane (CH4) represents a major product of organic matter decomposition in lakes. Once produced in the sediments, CH4 can be either oxidized or emitted as a greenhouse gas to the atmosphere. Lakes represent an important source of atmospheric CH4, but the relative magnitudes of the internal pathways that lead to CH4 emissions are not yet clear. We quantified internal cycling and methane emissions in three lakes during summer stratification. These methane budgets included: sediment release of CH4 at different depths; water column transport patterns and methane oxidation; methane storage in the water column; and methane emissions to the atmosphere by diffusion and ebullition. The contribution of CH4 carbon, via oxidation by methanotrophic bacteria, to pelagic food webs was also estimated. Despite the very low concentration of CH4 in surface waters, shallow, epilimnetic sediments were major contributors of CH4 to the atmosphere. While 51 - 80% of the CH4 produced in deep sediments was oxidized in the water column, most of the CH4 released from shallow sediment escaped oxidation and reached the atmosphere. Epilimnetic sediments accounted for 100% of CH4 emitted during summer stratification, and 14 - 76% considering the release of CH4 stored in deep water layers during lake circulation after the stratification period; diffusive emission accounted for 26 - 48% and ebullition the remainder. These results indicate that it is important to address transport rates of CH4 from the shallow sediment along with the production-consumption processes when trying to understand methane dynamics and the regulation of lake methane emissions.

33.

Bastviken, David

Stockholm University, Faculty of Science, Department of Geology and Geochemistry.

Abstract: Coastal sediments represent sites of major importance for many biogeochemical processes, including organic matter mineralisation. These sediments are frequently subjected to intermittent physical forcing resulting in resuspension, which potentially influences sediment processes. In this study we investigated how the frequency and duration of resuspension events affect organic matter mineralisation rates, by creating conditions where the resuspension effect was as isolated as possible from other factors possibly affecting the mineralisation rate. Results show that continuous resuspension or resuspension in 12 h intervals double the mineralisation rates compared to sediments not subjected to water turbulence (2.0 +/- 0.2 vs. 1.1 +/- 0.3 mu mol Sigma CO2 (g d.w.)(-1) d(-1)). However, when subjected to short resuspension events (5 s) once every 24 or 48 h the sediment mineralisation rate were enhanced even more, to 5.2 +/- 0.3 mu mol Sigma CO2 (g d.w.)(-1) d(-1). Longer intervals between resuspension events (72-96 h) did not affect the mineralisation rate compared to no water turbulence. This indicates that resuspension enhances mineralisation rates, and that even very short resuspension events can influence sediment carbon and nutrient cycling to a large extent if occurring often enough. Hence, sediment mineralisation rate measurements without resuspension may significantly underestimate mineralisation rates. However, given our results, it is possible that continuous low-level shear stress in coastal areas may be enough to stimulate mineralisation, and then specific events with increased shear stress and resuspension may not cause any additional enhancement. Therefore, to illuminate potential effects of resuspension on mineralisation under field conditions, more information about the level of shear stress that is required to affect mineralisation rates is needed.

34.

Bastviken, David

et al.

Stockholm University, Faculty of Science, Department of Geology and Geochemistry.

Svensson, Teresia

Karlsson, Susanne

Sanden, Per

Stockholm University, Faculty of Science, Department of Geology and Geochemistry.

Old assumptions that chloride is inert and that most chlorinated organic matter in soils is anthropogenic have been challenged by findings of naturally formed organochlorines. Such natural chlorination has been recognized for several decades, but there are still very few measurements of chlorination rates or estimates of the quantitative importance of terrestrial chlorine transformations. While much is known about the formation of specific compounds, bulk chlorination remains poorly understood in terms of mechanisms and effects of environmental factors. We quantified bulk chlorination rates in coniferous forest soil using Cl-36-chloride in tracer experiments at different temperatures and with and without molecular oxygen (O-2). Chlorination was enhanced by the presence of O-2 and had a temperature optimum at 20 degrees C. Minimum rates were found at high temperatures (50 degrees C) or under anoxic conditions. The results indicate (1) that most of the chlorination between 4 and 40 degrees C was biotic and driven by O-2 dependent enzymes, and (2) that there is also slower background chlorination occurring under anoxic conditions at 20 degrees C and under oxic conditions at 50 degrees C. Hence, while oxic and biotic chlorination clearly dominated, chlorination by other processes including possible abiotic reactions was also detected.

Inorganic chlorine (i.e. chloride; Cl-in) is generally considered inert in soil and is often used as a tracer of soil and ground water movements. However, recent studies indicate that substantial retention or release of Cl-in can occur in soil, but the rates and processes responsible under different environmental conditions are largely unknown. We performed Cl-36 tracer experiments which indicated that short-term microbial uptake and release of Cl-in, in combination with more long-term natural formation of chlorinated organic matter (Cl-org), caused Cl-in imbalances in coniferous forest soil. Extensive microbial uptake and release of Cl-in occurred over short time scales, and were probably associated with changes in environmental conditions. Up to 24% of the initially available Clin within pore water was retained by microbial uptake within a week in our experiments, but most of this Cl-in, was released to the pore water again within a month, probably associated with decreasing microbial populations. The natural formation of Clorg resulted in a net immobilization of 4% of the initial pore water Clin over four months. If this rate is representative for the area where soil was collected, Clorg formation would correspond to a conversion of 25% of the yearly wet deposition of Cl-in. The study illustrates the potential of two Clin retaining processes in addition to those previously addressed elsewhere (e.g. uptake of chloride by vegetation). Hence, several processes operating at different time scales and with different regulation mechanisms can cause Clin imbalances in soil. Altogether, the results of the present study (1) provide evidence that Cl-in cannot be assumed to be inert in soil, (2) show that microbial exchange can regulate pore water Cl-in, concentrations and (3) confirm the controversial idea of substantial natural chlorination of soil organic matter.

Several studies have demonstrated that extensive formation of organically bound chlorine occurs both in soil and in decaying plant material. Previous studies suggest that enzymatic formation of reactive chlorine outside cells is a major source. However, the ecological role of microbial-induced extracellular chlorination processes remains unclear. In the present paper, we assess whether or not the literature supports the hypothesis that extracellular chlorination is involved in direct antagonism against competitors for the same resources. Our review shows that it is by no means rare that biotic processes create conditions that render biocidal concentrations of reactive chlorine compounds, which suggest that extracellular production of reactive chlorine may have an important role in antagonistic microbial interactions. To test the validity, we searched the UniprotPK database for microorganisms that are known to produce haloperoxidases. It appeared that many of the identified haloperoxidases from terrestrial environments are originating from organisms that are associated with living plants or decomposing plant material. The results of the in silico screening were supported by various field and laboratory studies on natural chlorination. Hence, the ability to produce reactive chlorine seems to be especially common in environments that are known for antibiotic-mediated competition for resources (interference competition). Yet, the ability to produce haloperoxidases is also recorded, for example, for plant endosymbionts and parasites, and there is little or no empirical evidence that suggests that these organisms are antagonistic.

This issue of the GFF is dedicated to Professor Maurits Lindström on the occasion of his 75th birthday by students, colleagues, and friends in recognition of his profound impact on the Science of Geology as researcher and teacher during more than half a century.

41. Billström, Kjell

et al.

Broman, Curt

Stockholm University, Faculty of Science, Department of Geology and Geochemistry.

Jonsson, Erik

Recio, Clemente

Boyce, Adrian

Torssander, Peter

Stockholm University, Faculty of Science, Department of Geology and Geochemistry.

The Cretaceous/Paleogene (K/Pg) mass extinction seriously affected the marine pelagic ecosystem causing >90% loss of planktonic foraminifera species. Surface to deep-ocean foraminiferal d13C gradients and carbonate accumulation show that the extinctions coincided with a crash in organic matter flux to the sea floor that disrupted carbon cycling and took 3Myr to recover. Establishing the evolutionary and ecological response of the plankton through this recovery is important for understanding the role of the pelagic ecosystem in marine carbon cycling. Here we present new multispecies foraminiferal stable isotope data and planktic shell size distributions from a new, well-dated and continuous Atlantic deep sea core. The data document the evolution and diversification of photosymbiosis (thought to be an adaptation to low nutrient pelagic environments) in Paleocene planktonic species 3 million years after the K/Pg extinction when the pelagic carbon system recovered to a pre-K/Pg state and Oligotropic conditions returned. The data show that the geochemical signature of photosymbiosis evolved in an initially thermocline dwelling species, Preamurica pseudoinconstans, that started migrating to the shallower photic levels during later life stages. Initially appearing less than 1 myr after the K/ Pg extinction, symbiosis as an ecological strategy did not become important for a further 2 million years when the genus Morozevlla underwent major diversification, probably in response to an expanding ecologic opportunity that in turn resulted from final recovery of the marine carbon cycle.

43. Björck, S

et al.

Backman, Jan

Stockholm University, Faculty of Science, Department of Geology and Geochemistry.

Seafloor mapping of the central Lomonosov Ridge using a multibeam echo-sounder during the Beringia/Healy–Oden Trans-Arctic Expedition (HOTRAX) 2005 shows that a channel across the ridge has a substantially shallower sill depth than the 2500m indicated in present bathymetric maps. The multibeam survey along the ridge crest shows a maximum sill depth of about 1870 m. A previously hypothesized exchange of deep water from the Amundsen Basin to the Makarov Basin in this area is not confirmed. On the contrary, evidence of a deep-water flow from the Makarov to the Amundsen Basin was observed, indicating the existence of a new pathway for Canadian Basin Deep Water toward the Atlantic Ocean. Sediment data show extensive current activity along the ridge crest and along the rim of a local Intra Basin within the ridge structure.

It is suggested that the overall understanding of the general hydrogeochemistry of a region is best understood from a landscape perspective. If so, this can provide useful information when planning monitoring programmes and influence of human activity. In this thesis the influence of landscape properties on iron (Fe) and manganese (Mn) is investigated.

Iron and manganese are abundant in the Earth’s crust but occur in relatively low concentrations in most aquatic systems, due to the low solubility of their thermodynamically stable oxidation states (Fe(III) and (Mn(IV)). The hydrogeochemistry of iron and manganese is important, since their naturally occurring oxyhydroxides exhibit a strong adsorption affinity for trace elements. Moreover, the redox transformations of iron and manganese occur at pH and Eh (redox potential) boundaries found in natural waters.

We investigated the hydrogeochemistry of iron and manganese in a boreal stream network of 15 streams, located in Västerbotten, Sweden. Water samples were collected on a frequent basis during 2004 and 2005, from 15 sub-catchments of the Krycklan catchment (67 km2). Total (unfiltered) and dissolved (<0.4µm) concentrations of iron and manganese were used to investigate the influence of landscape types (i.e. percentage cover of wetlands and forest) on the spatial and temporal variations of these elements.

We found that iron correlates significantly with percentage of wetland and also with dissolved organic carbon (DOC). For manganese we did not observe a significant correlation with wetlands, which indicates that this element is less dependent on organic matter in comparison to iron. In particular, the correlation of the Fe/Al ratio to wetlands was highly significant (r2=0.92, p<0.01). However, principal component analyses indicate that iron, during peak discharge at spring flood, is not correlated with wetlands. During this period iron instead correlates with soil variables (i.e. silt) which highlights the importance of particulates during high discharge events.

Since the naturally occurring oxyhydroxides have a strong adsorption affinity for other trace elements it is of great importance to further increase the knowledge of how these elements interact with iron and manganese in relation to the landscape composition. Further analyses of relations between trace metals (e.g. Cd, Co, Cr, Cu, Pb), and iron and manganese, but also between trace metals and landscape composition, will highlight the importance of studying the hydrogeochemistry from a landscape perspective.

47.

Björkvald, Louise

Stockholm University, Faculty of Science, Department of Geology and Geochemistry.

The transport of elements by streams from headwater regions to the sea is influenced by landscape characteristics. This thesis focuses on the influence of landscape characteristics (e.g. proportion of wetland/forest coverage) on temporal and spatial variations of Fe, Mn, S and trace elements (As, Co, Pb) in streams located in northern Sweden, a boreal region characterized by coniferous forests and peat wetlands.

Water samples from a network of 15 streams revealed a different hydrogeochemistry in forested catchments compared to wetland catchments. The temporal variation was dominated by spring flood, when concentrations of Fe, Mn and trace elements increased in forested headwaters. However, in streams of wetland catchments concentrations decreased, but Pb concentrations were higher in comparison to other streams. Both Fe and Pb showed positive correlations with wetland area, while Co correlated with forest coverage. The anthropogenic contribution of As and Pb appear to be larger than the supply from natural sources.

During spring flood SO42- decreased in most streams, although concentrations increased in streams of wetland catchments. Concentrations of SO42- were higher in streams of forested catchments than in wetland dominated streams, the former being net exporters of S and the latter net accumulators. Isotope values of stream water SO42- (δ34SSO4) were close to that of precipitation during spring flood, indicating that the major source of S is from deposition. The results show that, although emissions of anthropogenic S have been reduced, there is still a strong influence of past and current S deposition on runoff in this region.

In conclusion, wetlands are key areas for the hydrogeochemistry in this boreal landscape. The findings emphasize the importance of understanding stream water chemistry and element cycling from a landscape perspective. This may be important for predicting how boreal regions respond to environmental disturbances such as climate change.

We studied temporal and spatial variations of trace metal (TM) concentrations (As, Cd, Co, Cr, Cu, Ge, La, Ni, Pb, Rb, Sc, and Y) in stream water and their correlation with catchment properties (i.e. coverage of wetland and forest), but also with Fe and Mn. During 2004 and 2005 water samples were collected from 10 streams (0.13 km2 to 67 km2) in the Krycklan Catchment Study, a boreal stream network in northern Sweden. Since spring snowmelt is the most important hydrological event, the monthly sampling was intensified during spring flood (April-May) when samples were collected every second day. Total and dissolved (<0.4µm) concentrations of Fe and Mn were determined by ICP-OES. Dissolved concentrations of TM were determined by ICP-MS.

Preliminary results show a seasonal variation for all TM, in particular during spring flood. In forested catchments most TM concentrations increased at spring flood, but for Rb and Sc a decrease was observed. Conversely, in wetland influenced catchments the opposite seasonal variation was observed, i.e. concentrations of all TM decreased by a factor of 2 to 3. The seasonal variation of Fe shows a similar pattern to many TM, due to the association of TM to Fe oxyhydroxides. In particular, Fe correlates significantly with Cr and Pb in a forested headwater stream (r2=0.77 and r2=0.71, respectively, p<0.05). In the wetland headwater stream similar correlations between Fe and TM are found, but DOC also correlates significantly with As, Cd, Ni, and Pb (r2=0.92, p<0.05).

A significant negative correlation (p<0.05) was observed between coverage of wetlands and average concentrations of Cr, Cu, Ge, Ni, Sc and Y. The results indicate that wetlands act as sinks for these elements. Alternatively, there is a source limitation in wetlands and that increased concentrations during base flow are due to mineral groundwater influence. Positive correlation with wetland coverage was only observed for Pb (r2=0.79, p<0.05), indicating that wetlands acts as a source for this element. Sulfate concentrations correlated negatively (r2=0.97, p<0.05) with increasing coverage of wetlands, which highlights the importance of sulfate reduction within wetland areas.

This study emphasizes the importance of considering stream water chemistry from a landscape perspective.

49.

Björkvald, Louise

et al.

Stockholm University, Faculty of Science, Department of Geology and Geochemistry.

Stream water from a stream network of 15 small boreal catchments (0.03–67 km2) in northern Sweden was analyzed for unfiltered (total) and filtered (<0.4 μm) concentrations of iron (Fetot and Fe<0.4) and manganese (Mntot and Mn<0.4). The purpose was to investigate the temporal and spatial dynamics of Fe, Mn and dissolved organic carbon (DOC) as influenced by snow melt driven spring floods and landscape properties, in particular the proportion of wetland area. During spring flood, concentrations of Fetot, Fe<0.4, Mntot, Mn<0.4 and DOC increased in streams with forested catchments (<2% wetland area). In catchments with high coverage of wetlands (>30% wetland area) the opposite behavior was observed. The hydrogeochemistry of Fe was highly dependent on wetlands as shown by the strong positive correlation of the Fetot/Altot ratio with wetland coverage (r2 = 0.89, p < 0.001). Furthermore, PCA analysis showed that at base flow Fetot and Fe<0.4 were positively associated with wetlands and DOC, whereas they were not associated during peak flow at spring flood. The temporal variation of Fe was likely related to varying hydrological pathways. At peak discharge Fetot was associated with variables like silt coverage, which highlights the importance of particulates during high discharge events. For Mn there was no significant correlation with wetlands, instead, PCA analysis showed that during spring flood Mn was apparently more dependent on the supply of minerogenic particulates from silt deposits on the stream banks of some of the streams. The influence of minerogenic particulates on the concentration of, in particular, Mn was greatest in the larger, lower gradient streams, characterized by silt deposits in the near-stream zone. In the small forested streams underlain by till, DOC was of greater importance for the observed concentrations, as indicated by the positive correlation of both Fetot and Fe<0.4 with DOC (r2 = 0.77 and r2 = 0.76, p < 0.001) at the smallest headwater forest site. In conclusion, wetland area and DOC were important for Fe concentrations in this boreal stream network, whereas silt deposits strongly influenced Mn concentrations. This study highlights the importance of studying stream water chemistry from a landscape perspective in order to address future environmental issues concerning mobility of Fe, Mn and associated trace metals.

Despite reduced anthropogenic deposition during the last decades, deposition sulphate may still play an important role in the biogeochemical cycles of S and many catchments may act as net sources of S that may remain for several decades. The aim of this study is to elucidate the temporal and spatial dynamics of both SO42- and delta S-34(SO4) in stream water from catchments with varying percentage of wetland and forest coverage and to determine their relative importance for catchment losses of S. Stream water samples were collected from 15 subcatchments ranging in size from 3 to 6780 ha, in a boreal stream network, northern Sweden. In forested catchments (2% wetland cover) S-SO42- concentrations in stream water averaged 1.7 mg L-1 whereas in wetland dominated catchments (30% wetland cover) the concentrations averaged 0.3 mg L-1. A significant negative relationship was observed between S-SO42- and percentage wetland coverage (r(2) = 0.77, p 0.001) and the annual export of stream water SO42- and wetland coverage (r(2) = 0.76 p 0.001). The percentage forest coverage was on the other hand positively related to stream water SO42- concentrations and the annual export of stream water SO42- (r(2) = 0.77 and r(2) = 0.79, respectively). The annual average delta S-34(SO4) value in wetland dominated streams was +7.6%omicron. and in streams of forested catchments +6.7%omicron. At spring flood the delta S-34(SO4) values decreased in all streams by 1%omicron to 5%omicron. The delta S-34(SO4) values in all streams were higher than the delta S-34(SO4) value of +4.7%omicron in precipitation (snow). The export of S ranged from 0.5 kg S ha(-1) yr(-1) (wetland headwater stream) to 3.8 kg S ha(-1) yr(-1) (forested headwater stream). With an average S deposition in open field of 1.3 kg S ha(-1) yr(-1) (2002-2006) the mass balance results in a net export of S from all catchments, except in catchments with 30% wetland. The high temporal and spatial resolution of this study demonstrates that the reducing environments of wetlands play a key role for the biogeochemistry of S in boreal landscapes and are net sinks of S. Forested areas, on the other hand were net sources of S.